1. Field of the Invention
The present invention relates to a suction nozzle and particularly to the art of improving the durability of a suction nozzle.
2. Discussion of Related Art
A suction nozzle is used to suck and hold an object, such as an electric component (EC), so as to mount the EC on a printed wiring board (PWB) as a sort of circuit substrate. The suction nozzle includes a nozzle portion having an end surface which functions as a suction surface, and a suction passage which opens in the suction surface. An image of the EC held by the suction nozzle may be taken so that image data representing the taken image are processed to determine a position of the EC held by the nozzle. In the case where a silhouette image of the EC is taken, the suction nozzle may additionally include a light-radiating portion which radially outwardly projects from a base portion thereof and has a light-radiating surface from which a light, such as a visible light or an ultraviolet light, is emitted. If a shadow of the suction nozzle overflows that of the EC, then it will be difficult to process the taken silhouette image, which will lead to lowering an accuracy with which a position of the EC held by the nozzle is determined. To avoid this problem, it has been a general practice to use a suction nozzle whose size is smaller than that of an EC. However, in a special case where an EC is very small, a user cannot help using a suction nozzle whose size is greater than that of the EC. In this case, if the suction passage of the nozzle portion may not be completely closed by the EC, the EC may not be completely held by the suction nozzle, so that the suction nozzle may fail to hold the EC, or the EC may fall off the suction nozzle. This is true with a case where a position of an EC held by a suction nozzle is determined based on a reflection-light image of the EC and a case where no image is taken to determine a position of an EC held by a suction nozzle.
Thus, a small EC is necessarily held by a suction nozzle including a nozzle portion whose diameter is small. However, when the suction nozzle holds an EC or mounts the EC, the nozzle portion receives some load. Conventionally, this load causes bending of the nozzle portion, thereby reducing the life expectancy of the suction nozzle. This leads to increasing the frequency of exchanging of suction nozzles, thereby increasing the running cost of the mounting apparatus. In addition, since the operation efficiency of the mounting apparatus lowers because of the frequent exchanging of suction nozzles, the production efficiency thereof also lowers. Moreover, if a suction nozzle including a small-diameter nozzle portion is used, the nozzle portion easily vibrates, which may lead to lowering an accuracy with which an EC held by the suction nozzle is mounted on a PWB.
The present invention provides a suction nozzle and an EC-position detecting apparatus that have each feature described below. An EC may be, in particular, an electronic component. The following features are described, like claims, in respective paragraphs that are given respective sequential numbers. Any feature that includes another feature shall do so by referring to the number given to the latter feature. However, the following features and the appropriate combinations thereof are just examples to which the technical features, and the combinations thereof, described in the specification are by no means limited. In addition, in the case where one feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed in the one feature. That is, it is possible to select and employ only a portion (one, two, . . . , but not all) of those items.
(1) According to a first feature of the present invention, there is provided a suction nozzle for applying a suction to an object and thereby holding the object, the suction nozzle including a nozzle portion having an end surface, and a suction passage formed in the nozzle portion and opening in the end surface thereof, the end surface providing a suction surface that applies the suction to the object and thereby holds the object, wherein the improvement comprises at least a free end portion of the nozzle portion having a shape whose diameter gradually increases in a direction from the end surface thereof toward a base end thereof opposite to the end surface.
Since at least the free end portion of the nozzle portion has the shape whose diameter gradually increases in the direction from the end surface toward the base end, the free end portion may be so thin that the contour of the end surface may not overflow that of the object, or an amount of overflow of the former contour may be little, whereas the base end of the nozzle portion may be thicker than the free end portion thereof. Therefore, the nozzle portion can enjoy an increased flexural strength and an improved durability. In addition, the nozzle portion can enjoy a high flexural rigidity, in spite of having the thin free end portion, so that the nozzle portion may not be easily vibrated. Thus, the suction nozzle can enjoy an improved accuracy with which the nozzle mounts the object, such as an electric component (EC), on a circuit substrate such as a printed wiring board (PWB). In order to improve the flexural strength and rigidity of the nozzle portion, it is desirable that the nozzle portion have a shape whose diameter gradually increases from the end surface to the base end, i.e., as a whole, as recited in the second feature (2).
(2) According to a second feature of the present invention that includes the first feature (1), the nozzle portion has a shape whose diameter gradually increases from the end surface to the base end.
(3) According to a third feature of the present invention that includes the first or second feature (1) or (2), the nozzle portion has a tapered shape whose diameter linearly increases in the direction from the end surface to the base end.
There are some cases where it is desirable that the nozzle portion have a shape whose diameter nonlinearly changes depending upon a shape, a size, a position, etc. of a light emitter. However, in many cases, the nozzle portion whose diameter linearly changes can achieve its aim. In addition, the suction nozzle having the latter nozzle can be easily produced.
(4) According to a fourth feature of the present invention that includes any one of the first to third features (1) to (3), the suction nozzle further includes a light radiating portion extending radially outwardly from a base end portion of the nozzle portion, and having a light radiating surface which radiates a light.
(5) According to a fifth feature of the present invention that includes the fourth feature (4), at least a radially outer portion of the light radiating surface is so inclined that a distance of the radially outer portion from the end surface of the nozzle portion in a direction parallel to an axis line thereof gradually increases in a radially inward direction.
Since at least the radially outer portion of the light radiating surface is so inclined that the distance of the radially outer portion from the end surface of the nozzle portion in the direction parallel to the axis line thereof gradually increases radially inward direction, the light radiated from the light radiating surface can easily gather toward the central axis line of the suction nozzle. Thus, the object can have a uniform, light background, and accordingly an excellent silhouette image of the object can be taken. In particular, in the case where an outer circumferential surface of the nozzle portion provides a reflection surface, as recited in the eighth feature (8), the light radiated from the light radiating surface can easily gather toward the reflection surface.
(6) According to a sixth feature of the present invention that includes the fourth or fifth feature (4) or (5), an entirety of the light radiating surface is so inclined that the distance of the light radiating surface from the end surface of the nozzle portion gradually increases in the radially inward direction.
(7) According to a seventh feature of the present invention that includes any one of the fourth to sixth features (4) to (6), the light radiating surface has a tapered shape whose diameter linearly decreases as a distance of the light radiating surface from the end surface of the nozzle portion in the direction parallel to the axis line thereof increases.
There are some cases where it is desirable that the light radiating surface have a shape whose diameter nonlinearly changes depending upon a shape, a size, a position, etc. of the nozzle portion or a light emitter. However, in many cases, the light radiating surface whose diameter linearly changes can achieve its aim. In addition, the suction nozzle having the latter light radiating surface can be easily produced.
(8) According to an eighth feature of the present invention that includes any one of the first to seventh features (1) to (7), an outer circumferential surface of at least the free end portion of the nozzle portion that has the shape whose diameter gradually increases provides a reflection surface which reflects the light radiated by the light radiating surface.
Since the outer circumferential surface of at least the free end portion of the nozzle portion that has the shape whose diameter gradually increases provides a reflection surface, the light radiated from the light radiating surface is reflected by the reflection surface toward the object held by the suction surface. Thus, the object held by the suction surface can have a uniform background.
(9) According to a ninth feature of the present invention that includes any one of the fourth to eighth features (4) to (8), the light radiating surface comprises a fluorescent surface which absorbs an ultraviolet light emitted by a light emitter in the direction from the end surface of the nozzle portion toward the base end thereof, and radiates a visible light.
If this suction nozzle is used with an image taking device including at least one of a filter which cuts off an ultraviolet light and allows passing of a visible light, and an image-taking element which is not sensitive to an ultraviolet light and is sensitive to a visible light, the silhouette image of the object can be prevented from being lighted by the ultraviolet light reflected by the object and accordingly the accuracy of detection of the contour of the object can be effectively prevented from being lowered.
(10) According to a tenth feature of the present invention that includes any one of the fourth to eighth features (4) to (8), the light radiating surface comprises a reflection surface which reflects a light emitted by a light emitter in the direction from the end surface of the nozzle portion toward the base end thereof.
In this case, it is desirable to employ a shield member which prevents the object from being exposed to the light such as a visible light or an ultraviolet light.
(11) According to an eleventh feature of the present invention that includes any one of the fourth to eighth features (4) to (8), the light radiating portion comprises a light emitting portion which incorporates a light source, and the light radiating surface radiates a light emitted by the light source.
(12) According to a twelfth feature of the present invention, there is provided an apparatus for detecting a position of an electric component, comprising a suction nozzle according to any one of the first to eleventh features (1) to (11), the suction nozzle holding the electric component; an annular light source which is provided at a position where the annular light source is caused, at at least one timing, to be concentric with the suction nozzle, and which radiates a light along the nozzle portion; an image taking device which takes an image of the electric component held by the nozzle portion, and a background of the electric component, at the at least one timing; and an image processing device which processes image data representing the image taken by the image taking device and thereby determines the position of the electric component held by the nozzle portion.
(13) According to a thirteenth feature of the present invention that includes the twelfth feature (12), respective dimensions and positions of the nozzle portion, the light radiating surface, and the light source are so determined that a difference between a greatest brightness, and a smallest brightness, of the background of the electric component in the image taken by the image taking device is not greater than 25% of the greatest brightness.
The greatest brightness and smallest brightness of the background may be selected from respective brightness values of respective picture elements or pixels of the background, or respective average brightness values of respective unit areas of the background. Each unit area may be four picture elements (2xc3x972), nine picture elements (3xc3x973), or thirteen picture elements (1, 3, 5, 3, and 1 elements arranged along one axis). The respective picture elements or pixels of the background may correspond to respective image-taking elements (e.g., CCDs) of the image taking device.
If the difference between the greatest and smallest brightness values of the background is great, it is difficult to accurately detect the boundary between the image of the electric component (EC) and the image of the background, i.e., the contour of the EC. Though the unevenness of brightness of the background image can be dealt with to some extent by image-processing techniques, it is desirable that respective dimensions and positions of the nozzle portion, the light radiating surface, and the light source be so determined that the difference between the greatest and smallest brightness values of the background image is not greater than 25% of the greatest brightness, more preferably not greater than 20%, and most preferably not greater than 15%.